Hydraulic sequential control systems



F. J- FUELL. ETAL 3 Sheets-Sheet 1 a m N am a a i o m u M P .53 w u NN mm I u E 2 Emma BY mam. new, iv-me. avimm Avmm v Sept. 3, 1968 HYDRAULIC SEQUENTIAL CONTROL SYSTEMS Filed Mai-en 24, 1965 F. J. FUELL ETAL 3,399,601

HYDRAULIC SEQUENTIAL CONTROL SYSTEMS Sept. 3, 1968 3 Sheets-Sheet 5 Filed March 24, 1965 Si 60 A A F/el Devan-mes Joan L.Fbw|.a2 Fezbamcu JJ UELL. Fem: G. Maw-res Bee-m: Gpmzmus Aw-mways HYDRAULIC SEQUENTIAL CONTROL SYSTEMS Frederick J. Fuel], Frank G. Mattos, John L. Fowler, and

Bertie G. Parlrins, Heston, England, assignors to Fairey Engineering Limited, Heston, England, a company of Great Britain Filed Mar. 24, 1965, Ser. No. 442,551 16 Claims. (Cl. 91-36) This invention relates to hydraulic systems :for automatically performing a cycle of operations. The invention is particularly, though not exclusively, concerned with a semi-automatic system of walking pit props.

Such systems have in general either been manually controlled, in which case it is necessary for a man to actuate a number of valves in succession in order to cause a set of pit props to move a step forward or backward, or have involved a costly and complicated fully automatic system. The present invention provides a system which saves almost as much time as the automatic system but is very much simpler.

According to one aspect of the present invention a hydraulic system for automatically performing a series of at least six operations, of which the first and third, the second and fifth, and the fourth and sixth are reversals of each other, includes two sequence controllers respectively serving to initiate the first three operations and the second three operations in sequence, and a reversing device for reversing the second and fifth operations, and means for actuating the first sequence controller and then the second sequence controller, with the reversing device in one position to initiate the operations in one sequence, and to actuate the second sequence controller and then the first sequence controller with the reversing device in the other position to initiate the operations in a different sequence.

Where the invention is applied to walking pit props various arrangements of props are possible. The simplest arrangement would be merely a front prop ram and a rear prop ram connected by a double-acting horizontal ram. In general, however, it will be preferable to employ front and rear left-hand prop rams connected to opposite ends of the piston rod of a double-acting horizontal ram, and front and rear right-hand prop rams connected to opposite ends of the cylinder.

In the former case the sequence of operations for a step forward would comprise lowering the front prop ram, extending the horizontal ram, raising the front prop ram, lowering the rear prop ram, contracting the horizontal ram and raising the rear prop ram. In order to take a step backwards it will be appreciated that the sequence of operations is not merely reversed. Thus it is necessary to lower the rear prop ram, extend the horizontal rarn, raise the rear pro-p ram, lower the front prop ram, contract the horizontal ram and raise the front prop ram.

Similarly in the case of the latter arrangement a forward step may comprise lowering the left-hand prop rams, actuating the horizontal ram to advance the lefthand props, raising the left-hand prop rams, lowering the right-hand prop rams, actuating the horizontal ram to advance the right-hand props, and raising the right-hand prop rams. Similarly to take a step backwards the sequence of operations in not merely the reverse of that required for a forward step.

In one form of the invention each sequence controller comprises a number of operating valves arranged in a row and a cam actuated by a hydraulic ram, which will Fe referred to as a sequence ram, to move along the row and actuate the valves in succession. Conveniently the valves Patented Sept. 3, 1968 are poppet valves which may be actuated by means of rocking tappets mounted in the path of the cam. The cam, which may be in the form of a roller, is conveniently mounted on a trigger lever so as to be retracted clear of the tappets during the return movement of the ram.

Conveniently the two sequence controllers are mounted alongside one another and they may be arranged so that during a complete cycle one first moves to its fully extended position in which it remains whilst the other then moves to its fully extended position, whereupon both sequence controllers return to their initial position. The arrival of the first sequence controller in its final position may actuate means, such as a microswitch, for initiating the movement of the second sequence controller.

It may be convenient, more especially for manual operation, to provide separate valves for independently lowering the two prop rams which normally move together, for example the two left-hand prop rams or the two righthand prop rams. Similarly for actuating the double-acting horizontal ram two poppet valves may be required. Accordingly each row of valves may comprise five valves of which the first two are connected respectively to the two prop rams associated with that sequence controller, the third and fourth are shared between the two controllers for actuating the horizontal ram, both the third valves being actuated by one sequence controller whilst both the fourth valves are actuated by the other, and the fifth valve being connected to both of the associated prop rams.

Means are preferably provided for ensuring that if the pressure should fail, so that one pair of prop rams is not fully raised at the end of one half cycle, the ensuing half cycle will not occur and hence the other pair of prop rams will not be lowered. Such means may conveniently include microswitches mounted so as normally to be actuated by the sequence controllers at the end of their travel but arranged to be retracted to an inoperative position by a spring or the like if the system pressure should fail.

The invention may be put into practice in various ways but one specific embodiment will now be described by way of example with reference to the accompanying drawing, in which FIGURE 1 is a somewhat diagrammatic side elevation of a double sequence controller with parts broken away to show its mechanism,

FIGURE 2 is a hydraulic circuit diagram, and

FIGURE 3 is an electrical circuit diagram.

The invention is illustrated as applied to a hydraulic system for automatically controlling a single cycle of operation of a set of walking pit props. Each set of pit props comprises a right-hand pair 11 and 12. one in front of the other connected to opposite ends of the piston rod 15 of a horizntal duble-acting ram, and a left-hand pair 13 and 14 connected to opposite ends of the cylinder 16.

The operator is provided with a pair of control panels each controlling a group of twenty-five sets of pit props one group extending one way from him and the other group extending the other way from him along the coal face. The control panel is provided with a selector switch for selecting a particular set, and sections for individual sets each comprising an advance button, a retreat button and indicating lamps. The operator selects each set of props in turn and presses the advance button whereupon the system automatically performs one cycle consisting of six or eight operations required to take one step forward, without further action on the part of the operator.

The control apparatus for each set comprises a double sequence controller, which may conveniently be strapped to one of the Walking unit ram bodies. The control unit comprises two rows of poppet valves each including five valves 21 to 25 and 31 to 35 which in normal operation are arranged vertically one above the other with their axes horizontal. Each sequence controller compries a sequence ram 41 or 42 the plunger 43 or 44 of which actuates the valves. At its end the plunger has a slot accommodating a pair of link plates 45 carrying a roller cam 46. Thus the link plates can rock about a transverse axis through that of the plunger, so that the roller can swing from a retracted position (shown in chain lines) in line with the plunger, to a projecting pOsitiOn (shown in full lines) in which it projects sideways from the plunger to actuate the valves.

Each valve is provided with a rocking tappet 47 or 47A mounted on a transverse shaft and having an actuating surface 50 bearing on the end of the poppet valve rod to open the poppet valve, against the action of a spring 51 tending to keep it closed. Each of the tappets 47 has a ramp surface 49 for engagement by the associated roller cam 46, but the tappets 47A have no ramp surface and are always clear of the path of the roller cam. As indicated diagrammatically in FIGURE 2, most of the rocking tappets 47 with individual stub shafts 52 one of which extends through the outside of the casing and is provided with a hexagonal recess to be engaged by a key for manual opening of the individual valve. In the two cases of the third and fourth valves, however, the tappets 47 and 47A of the two sequence controllers are mounted on a comon shaft 53 so as both to rock together, their arrangement being such that both the third valves 23 and '33 will be opened simultaneously by the sequence ram 42 but not by the other sequence ram 41, whilst both the fourth valves 24 and 34 will be opened by the sequence ram 41 but not by the sequence ram 42.

Above the first pair of rocking tappets 47 microswitches 59 and 60 are mounted so as to be respectively engaged by a step on each of the plungers 43, 44 to indicate that that plunger has started its outward travel. Similarly a pair of microswitches 62 are mounted so as to be both actuated by the end of the plunger 44 when. it reaches the end of its outward travel, and a second pair of microswitches 63 are similarly mounted for actuation by the end of the other plunger 43 at the end of its outward stroke. Both these pairs of microswitches 62 and 63, one pair for each sequence controller, are mounted on a common rocking lever 64 acted upon by a spring 65 tending to retract the microswitches clear of a dowel 66 which normally transmits movement from the plunger to the microswitches. A small piston 67, subjected to the hydraulic system pressure, acts on the rocking lever to overcome the spring 65 and hold the lever 64 against the dowel 66 with the microswitches in their operative position. Should the system pressure fail, the microswitches will be retracted to an inoperative position by the spring 65.

The unit also includes a pair of solenoid-controlled valves 68 and 69, and a reversing valve 70 which may conveniently be described in connection with the hydraulic system shown in FIGURE 2.

The hydraulic system Hydraulic presure fluid (for example at 3000 p.s.i.), is fed through conduits 72A, 72B indicated in chain lines from a supply 72 through a filter 73 and a variable restrictor valve 71 to the two solenoid-controlled valves 68 and 69, and is fed direct to the piston 67 which holds the microswitches in their operative position. The same supply of pressure fluid, bypasing the filter 73, is connected by conduits 72C, 72D to the valves 33, 34, 35 and 25 by a conduit 72B and to the return sides of the two sequence rams 41 and 42 where it acts on a reduced piston area, tending to withdraw the plungers 43, 44 inwardly. A low-pressure return or exhaust 75, 75A, indicated in broken lines, is also connected to the solenoid valves 68 and 69 and to the poppet valves 21, 22, 23, 24, 31 and 32.

Each of the poppet valves 21 and 22 is connected through a conduit 76A and a variable restrictor 76 to one of the associated prop rams 11 or 12, whilst both of the associated prop rams are connected through non-return valves 77 and a common conduit 77A to the poppet valve 25. The other two prop rams 13 and 14 are similarly connected to the poppet valves 31, 32 and 35. The poppet valves 33 and 24 are connected by a common conduit 78A through the reversing valve 70 to one end of the horizontal ram 16, whilst the poppet valves 23 and 34 are connected via a common conduit 78B through the reversing valve 70 to the opposite end of the horizontal ram 16. The reversing valve 70 is operated by pressure fluid delivered to opposite ends of it by conduits 78C, 78D. Thus one end is connected by the conduit 78D to one solenoidcontrolled valve 68 which is also connected to the operating cylinder of the associated sequence ram 41. The other end of the reversing valve 70 is connected by the conduit 78C to the other solenoid controlled valve 69 which is also connected to the operating cylinder of the other sequence cont-r01 ram 41.

Operation of the hydraulic system In order to etfect astep forward the solenoid-controlled valve 68 associated with the right-hand prop rams 11 and 12, which are connected to the valves 21 to 25, is opened.

This admits pressure fluid from supply 72 via conduits 72A, 72B and 78D to one end of the reversing valve 70, moving it to what will be termed its advance position (upwards in FIGURE 2), and at the same time it admits pres sure fluid to the advance sequence control ram 41 to cause it to move steadily outwards. The roller cam 46 carried by the ram plunger 43 first opens the valve 21 so as to release fluid from it and lower the associated prop 11. As the roller cam 16 passes on, the valve 21 closes and the valve 22 is opened the roller cam opens so as to lower the associated prop 12. When the roller cam 46 reaches the valve 23 nothing happens since the associated rocking tappet 47A has no cam ramp 49. On reaching the valve 24 the roller cam 46 opens both the valve 24 and the valve 34 whose rocking tappets 47 and 47A are mounted on the common shaft 53. The valve 24 when opened connects one end of the horizontal ram 16 through the reversing valve 70 via conduits 88A and 78A and 75 to exhaust, whilst the valve 34 when opened connects the other end of the ram 16 through the reversing valve 70 via conduits 88B, 78B and 72C to pressure fluid source 72. Accordingly the horizontal ram 16 moves so as to advance the right-hand props 11 and 12 (the props 13 and 14 being held stationary between the floor and roof). The roller cam 46 then allows the valves 24 and 34 to close, and opens the valve 25 admitting pressure fluid through conduits 72C and 77A to both the prop rams 11 and 12 so that they are raised again into contact with the roof.

At the end of its travel the sequencer ram plunger 43 actuates the microswitches 63 which, in a manner to be described below, initiate the movement of the second sequence ram 42 by opening the second solenoid controlled valve 69. This admits pressure fluid to the uppermost end of the reversing valve 70 (as seen in FIGURE 2) but as pressure fluid is already admitted to its other end the valve 70 is balanced and stays where it is in the advance position. Small relative pressure fluctuations may tend to move the valve 70 from the selected advance position, but these are neutralised by a friction device inherent in the piston proper.

In addition pressure fluid is admitted by the second solenoid valve 69 to the second sequence ram 42 which advances in a similar manner to the first. Its roller cam 46 first lowers the left hand props l3 and 14 successively by opening the valves 31 and 32. On arriving at the valve 33 it opens both the valves 33 and 23 so as to reverse the ends of the horizontal ram 16 to which pressure and exhaust are applied respectively. Accordingly the horizontal ram is moved in the opposite direction so as to advance the left hand props 13 and 14. The valves 23 and 33 are then allowed to close, the roller cam 46 passes the valves 24 and 34 without actuating them, since the tappet 47A of the valve 34 has no cam follower ramp, and finally opens the valve 35 so as to raise the left hand prop rams 13 and 14 into contact with the roof again. On arriving at the end of its travel the plunger 44 actuates the microswitches 62 and the fact that the pairs of microswitches 62 and 63 of both sequence rams 41 and 42 are then simultaneously actuated indicates that the cycle is complete, whereupon both solenoid valves switch over to exhaust and the sequence rams return to their initial positions.

The electric circuit As indicated in FIGURE 3 the electric circuit comprises three relays 80, 81 and 82 for ensuring that the cycle of operations described will occur automatically. The relays may be termed an advance relay 80, a retreat relay 81 and a stop relay 82. The advance relay coil 80 is connected across supply terminals 79 in series with holding contacts 80/1 of itself and normally-closed contacts 82/1 of the stop relay 82. The holding contacts 80/1 are shunted by an advance button 85 in series with normally-closed contacts 81/ 3 of the retreat relay 81 and by microswitch contacts 62/1 closed by the plunger of the second ram 42 at the end of its travel which may be referred to as its finish microswitch contacts 62/1. Connected across the supply in series with this microswitch are the other finish microswitch contacts 62/ 2 of the second ram plunger 44, the stop relay 82 and finish microswitch contacts 63/1 of the first ram 41.

Similarly the retreat relay 81 is connected in series with normally-closed contacts 82/2 of the stop relay and with its own holding contacts 81/ 1. The latter are shunted by finish microswitch contacts 63/2 of the first ram 41 and by a retreat button 86 in series with normally-closed contacts 80/3 of the advance relay 80. Each of the advance and retreat relays 80 and 81, with its stop contacts in series with it, is shunted by a red lamp 87, whilst a green lamp 88 is connected across the supply in series with the start microswitches 59 and 60 respectively; contacts which open when the plungers of their associated rams start to move and are connected in series so that the green lamp when illuminated indicates that neither ram 41 or 42 has moved. The advance relay 80 has contacts 80/2 connected across the supply in series with the advance solenoid-operated valve 68 whilst the retreat relay 81 has contacts 81/2 connected in series with the retreat solenoid operated valve 69.

Accordingly it is thought that the operation will be clear.

Operation When the advance button 85 is pressed it illuminates the advance red lamp 87 and energises the advance relay 80, which closes its holding contacts 80/1 and also opens its contacts 80/ 3 in series with the retract button so that that button is ineffective. In addition its contacts 80/2 energise the advance solenoid valve 68. As soon as the first sequence control ram 41 starts to move it extinguishes the green lamp.

At the end of its travel the first sequence ram 41 closes the finish microswitch contacts 63/2 shunting the retreat button 86 which illuminates the retreat red lamp 87 and energises the retreat relay 81. This closes its own holding contact 81/ 1, opens the normally-closed contacts 81/ 3 in series with the advance button 85 so that the advance button is ineffective, and its contacts 81/2 energise the retreat solenoid controlled valve 69, to start the second sequence ram 42.

When the second sequence ram 42 reaches the end of its travel both the microswitch contacts 62/2 and 63/1 in series with the stop relay 82 are closed and hence the stop relay 82 is energised, opening contacts 82/1 and 82/ 2 in series with both the advance and retreat relays so that both these relays are de-energised and both solenoid controlled valves 68 and 69 switch over to exhaust.

In order to make a retreating step it is only necessary to press the retreat button. This produces an analogous cycle of operations, but their sequence, though not accurately reversed, is modified so as to effect a retreating step.

Depression of the retreat button 86 illuminates the retreat red lamp 87 and energises the retreat relay 81, which closes its holding contacts 81/1 and also opens its contacts 81/ 3 in series with the retreat button so that that button is ineffecive. In addition its contacts 81/ 2 energise the retreat solenoid control valve 69, which is associated with the left-hand prop rams 13 and 14, which are connected to the valves 31 and 32, so that the valve is thus opened.

The opening of the control valve 69 admits pressure fluid from supply 72 via conduits 72A, 72B and 72C to one end of the reversing valve 70, moving it downwards, a sseen in FIGURE 2, and at the same time it admits pressure fluid to the retreat sequence control ram 42 to cause it to move steadily outwards. As soon as the lrst sequence control ram (which for a retreating step is ram 42) starts to move it extinguishes the green lamp by opening the contacts of the start microswitch 60. The roller cam 46 carried by the ram plunger 44 first opens the valves 31 and 32 so as to release fluid from them and lower the lefthand props 13 and 14. When the roller cam 46 reaches the valve 33 it opens both the valve 33 and the valve 23 whose rouking tappets 47 and 47A are mounted on a common shaft 53. The valve 33, when opened, connects one end of the horizontal ram 16 through the reversing valve 70 via conduits 88B, 70A, 78A, 72D and 72C to the pressure fluid source 72, whilst the valve 23 when opened connects the other end of the ram 16 through the reversing valve 70 via conduits 88A, 78B and 75 to exhaust. Accordingly, the horizontal ram 16 moves so as to move the left-hand props 13 and 14 in a retreating direction (the props 11 and 12 being held stationary between the floor and roof). The roller cam 46 then allows the valves 33 and 23 to close, and opens the valve 35 admitting pressure fluid through conduits 72C and 77A to both the prop rams 13 and 14 so that they are raised again into contact with the roof.

In similar manner to that for the advancing step procedure, at the end of its travel the first sequence ram 42 closes its finish microswitch contacts 62/2 and thereby automatically energises the other solenoid valve 68 which when opened admits pressure fiuid to the second sequence ram 41, and to the lowermost end of the reversing valve 70 (as seen in FIGURE 2). Since the pressure fluid is still admitted to the uppermost end via conduit 780 the valve member is balanced and stays in the lower position as shown in FIGURE 2.

The second sequence will proceed automatically as the ram plunger 44 moves outwardly in analogous fashion to that for the second sequence of the advancing step procedure, that is, the right-hand props Will first be lowered when the roller cam 46 opens the valves 21 and 22, nothing happens when the roller cam 46 reaches the valve 23 since the associated rocking tappet 47A has no cam ramp 49, and then on reaching the valve 24 the roller cam 46 opens both the valve 24 and the valve 34 thereby reversing the pressure and exhaust connections to the horizontal ram 16.

Accordingly the horizontal ram moves so as to move the right-hand props in a retreating direction, i.e. towards props 13 and 14 which are held stationary between the floor and roof. The props 11 and 12 are thereafter raised into contact with the roof when valve 25 is opened by the roller cam 46 of the ram plunger 44.

As with the advancing step, at the end of the travel of the ram 41 both microswitch contacts 62/1 and 63/1 are closed thereby energising the stop relay 82, and deenergising both the relays of the solenoid control valves 68 and 69 which are thus switched over to exhaust.

It will be appreciated that the invention is not restricted to the details of the specific embodiment described nor to the specific purpose of the latter. Thus the general principles of the invention may be employed for purposes other than walking pit props. For example for the control of machine tools.

What We claim as our invention and desire to secure by Letters Patent is:

1. A hydraulic system for automatically performing a series of at least six operations, comprising first and sec ond sequence controllers to initiate the first three operations and the second three operations in sequence, a reversing device for reversing a number of operations, and means for actuating the first sequence controller and then the second sequence controller, with the reversing device in one position, to initiate the operations in one sequence, and to actuate the second sequence controller and then the first sequence controller, with the reversing device in another position, to initiate the operations in a dilferent sequence.

2. A system as claimed in claim 1 which comprises a front prop ram and a rear prop ram connected by a double-acting horizontal ram, and the sequence of operations for a step forward comprises lowering the front prop ram, extending the horizontal ram, raising the front prop ram, lowering the rear prop ram, contracting the horizontal ram and raising the rear prop ram, whilst the sequence for a step backwards comprises lowering the rear prop ram, extending the horizontal ram, raising the rear prop ram, lowering the front prop ram, contracting the horizontal ram and raising the front prop ram.

3. A system as claimed in claim 1 which comprises front and rear left-hand prop rams and front and rear right-hand prop rams, the prop rarns on one side being connected to opposite ends of a piston rod of a doubleacting horizontal ram, and those on the other side being connected to opposite ends of a cylinder, and the sequence of operations for a forward step comprises lowering the prop rams on the one side, actuating the horizontal ram to advance the lowered props, raising those prop rams, lowering the prop rams on the other side, actuating the horizontal ram to advance the lowered props, and raising those prop rams, whilst for a step backwards the sequence comprises lowering the prop rams on one side, actuating the horizontal ram to retreat the lowered props, raising those prop rams, lowering the prop rams on the other side, actuating the horizontal rarn to retreat the lowered props and raising those prop rams.

4. A system as claimed in claim 1, in which each se quence controller comprises a plurality of operating valves arranged in a row and a cam actuated by a hydraulic ram as a sequence rarn, to move along the row and actuate the valves in succession.

5. A system as claimed in claim 1, in which each sequence controller comprises a plurality of operating valves arranged in a row and a cam actuated by a hydraulic ram as a sequence ram, to move along the row and actuate the valves in succession, the fluid fed to the sequence ram through flow restricting means to control its rate of movement.

6. A system as claimed in claim 1, in which each sequence controller comprises a plurality of operating valves arranged in a row and a cam actuated by a hydraulic ram as a sequence ra-m, to move along the row and actuate the valves in succession, the valves being poppet valves and are actuated by means of rocking tappets mounted in the path of the cam.

7. A system as claimed in claim I, in which each se quence controller comprises a plurality of operating valves arranged in a row and a cam actuated by a hydraulic ram as a sequence ram, to move along the row and actuate the valves in succession, the cam being mounted on a trigger lever so as to be retracted clear of the tappets during the return movement of the cam.

8. A system as claimed in claim 1, in which each sequence controller comprises a plurality of operating valves arranged in a row and a cam actuated by a hydraulic ram as a sequence ram, to move along the row and actuate the valves in succession, the cam being in the form of a roller.

9. A system as claimed in claim 1, in which each sequence controller comprises a plurality of operating valves arranged in a row and a cam actuated by a hydraulic ram as a sequence ram, to move along the row and actuate the valves in succession, the two sequence controllers being mounted alongside one another.

10. A system as claimed in claim 1, in which each sequence controller comprises a plurality of operating valves arranged in a row and a cam actuated by a hydraulic ram as a sequence ram, to move along the row and actuate the valves in succession, in which means are provided whereby the two sequence controllers are arranged so that during a complete cycle one first moves to its fully extended position, in which it remains whilst the other then moves to its fully extended position, whereupon both sequence controllers return to their initial position.

11. A system as claimed in claim 1, in which each sequence controller comprises a plurality of operating valves arranged in a row and a cam actuated by a hydraulic ram as a sequence mm, to move along the row and actuate the valves in succession, the first sequence controller, in its final position, actuating means as a micro-switch for initiating the movement of the second sequence controller.

12. A system as claimed in claim 1, in which each se quence controller comprises a plurality of operating valves arranged in a row and a cam actuated by a hydraulic ram as a sequence mm, to move along the row and actuate the valves in succession, and valves for independently lowering two prop rams which normally move together.

13. A system as claimed in claim 1, in which each sequence controller comprises a plurality of operating valves arranged in a row and a cam actuated by a hydraulic ram as a sequence ram, to move along the row and actuate the valves in succession, and two poppet valves for actuating the double-acting horizontal ram.

14. A system as claimed in claim 1, in which each sequence controller comprises a plurality of operating valves arranged in a row and a cam actuated by a hydraulic ram as a sequence ram, to move along the row and actuate the valves in succession, the row of valves comprises five valves of which the first two are connected respectively to the two prop rams associated with that sequence controller, the third and fourth are shared between the two controllers for actuating the horizontal ram, both the third valves being actuated by one sequence controller whilst both the fourth valves are actuated by the other, and the fifth valve being connected to both of the associated prop rams.

15. A system as claimed in claim 1, in which each sequence controller comprises a plurality of operating valves arranged in a row and a cam actuated by a hydraulic ram as a sequence ram, to move along the row and actuate the valves in succession, and means for ensuring that if the pressure should fail, so that one pair of prop rams is not fully raised at the end of one half cycle, the ensuing half cycle will not occur and the other pair of prop rams will not be lowered.

16. A system as claimed in claim 1, in which each sequence controller comprises a plurality of operating valves arranged in a row and a cam actuated by a hydraulic ram as a sequence ram, to move along the row and actuate the valves in succession, and means for ensuring that if the pressure should fail, so that one pair of prop rams is not fully raised at the end of one half cycle, the ensuing half cycle will not occur and the other pair of prop rams will not be lowered, the means referred to include micro-switches mounted so as normally to be actuated by the sequence controllers at the end of their travel by arranged to be retracted to an inoperative position by a spring or the like if the system pressure should fail.

References Cited UNITED STATES PATENTS Miedbrodt 9136 Olson 91-189 Goodrich 91-36 Seddon 91170 Bolton 91-187 10 PAUL E. MASLOUSKY, Primary Examiner. 

1. A HYDRAULIC SYSTEM FOR AUTOMATICALLY PERFORMING A SERIES OF AT LEAST SIX OPERATIONS, COMPRISING FIRST AND SECOND SEQUENCE CONTROLLERS TO INITIATE THE FIRST THREE OPERATIONS AND THE SECOND THREE OPERATIONS IN SEQUENCE, A REVERSING DEVICE FOR REVERSING A NUMBER OF OPERATIONS, AND MEANS FOR ACTUATING THE FIRST SEQUENCE CONTROLLER AND THEN THE SECOND SEQUENCE CONTROLLER, WITH THE REVERSING DEVICE IN ONE POSITION, TO INITIATE THE OPERATIONS IN ONE SEQUENCE, AND TO ACTUATE THE SECOND SEQUENCE CONTROLLER AND THEN THE FIRST SEQUENCE CONTROLLER, WITH THE REVERSING DEVICE IN ANOTHER POSITION, TO INITIATE THE OPERATIONS IN A DIFFERENT SEQUENCE. 